April 10, 2013

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As discussed in Stronger Than Steel: Spider Silk DNA and the Quest for Better Bulletproof Vests, Sutures, and Parachute Rope, spider silk is a protein. A protein is a type of polymer. Polymers are substances in which the molecules line up like beads on a long string. In this video, a scientist discusses spider silk as a polymer:

How polymers behave depend on their molecules and how they’re put together. Spider silk is strong and stretchy. But polymers can also be hard, bouncy, or…goopy.

Cornstarch, a polymer, comes powdered in a box. If you add water to it, you’ll get this weird goopy stuff. Add one part water to two parts cornstarch (for instance, one cup of water to two cups of cornstarch.) Now, watch how weirdly the substance behaves. With your fingers, stir the goop slowly and then quickly. You’ll notice that the faster the goop is stirred, the more solid it becomes. Scoop some up and let it drip off your fingers. At first, it flows like a liquid. But as the dripping liquid picks up speed, it stops. Now it’s acting like a solid. The faster the goop moves, the, er, slower it moves. This is because of those long strands of molecules that make up polymers. When the molecules are agitated quickly, they get tangled up. When agitated more slowly, they do not become tangled and can move more freely.

By the way, did the scenario above seem familiar? Have you ever been stuck in quicksand? Then you know that the more you struggle, the more solid quicksand becomes, thus trapping you. And you also know, having survived, that if you relax, the quicksand becomes more liquid, allowing you to slowly crawl out. But what you might NOT have known while fighting for your life is that quicksand is a polymer!

Important! Don’t pour the goop down the drain! It will mix with the water from your sink, and clog the pipe. Either mix the goop in a disposable container, or let the mixture dry out and then scrape it into the trash.

Here are a couple links with more information and experiments regarding polymers:

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About Bridget Heos

Bridget Heos has written many nonfiction books for young people including her first Scientists in the Field book Stronger Than Steel: Spider Silk DNA and the Quest for Better Bulletproof Vests, Sutures, and Parachute Rope, with photographs by Andy Comins. She lives in Kansas City, Missouri with her family. Visit her website at www.authorbridgetheos.com.